Field of the Invention
The present invention relates to an image processing apparatus.
Priority is claimed on Japanese Patent Application No. 2014-101681, filed May 15, 2014, the content of which is incorporated herein by reference.
Description of Related Art
In image processing apparatuses such as digital cameras, image compression technology is adopted in accordance with recently increasing pixel density. In addition, although technology for compressing YCbCr data represented, by Joint Photographic Experts Group (JPEG) or the like is generally known in relation to image compression, a large number of technologies for compressing RAW data have also recently been adopted.
In addition, it is known that compression is efficiently enabled by dividing image data into a plurality of image regions and selecting a compression parameter in each image region to perform a compression process (for example, see the publication of Japanese Unexamined Patent Application, First Publication No. 2006-332955).
In the content disclosed in the publication of Japanese Unexamined Patent Application, First Publication No. 2006-332955, as shown in FIG. 20, a frame is divided into rectangular regions each having 10 pixels×10 pixels, and RAW data is compressed for every rectangular region. It is possible to perform an optimum compression process for every rectangular region by compressing data for every rectangular region in this manner. Thus, a more efficient compression process is possible. However, because the compression process is performed for every rectangular region, image data near a boundary of the rectangular region is likely to be discontinuous. As a result, an unintended pattern may appear near the boundary of the rectangular region.
In recent years, the high pixel density has been used increasingly for moving images as well and the number of cases in which compression technology is adopted for moving images is increasing. In such cases, degradation of image quality that is inconspicuous in still images may appear in moving images. In particular, in moving images in which motion between frames is small, image degradation near a boundary tends to appear as flickering.
Therefore, technology capable of reducing degradation of image quality near a boundary of an image region by shifting a separating position of the image region in a horizontal or vertical direction when image data is divided into a plurality of image regions and a compression process is performed for every image region is known (for example, see the publication of Japanese Unexamined Patent Application, First Publication No H04-26904).
In the content disclosed in the publication of Japanese Unexamined Patent Application, First Publication No. H04-269084, as shown in FIGS. 21A and 21B, degradation of image quality near a boundary of a rectangle is reduced by separating a frame into rectangular blocks, alternately shifting every line in a horizontal or vertical direction, and shifting a boundary portion of the rectangle with a previous line.
Also, in the method disclosed in the publication of Japanese Unexamined Parent Application, First Publication. No. H04-269084, the reduction effect of image quality degradation near the boundary of the rectangle may be weakened because there are a dense portion and a sparse portion of a boundary position of a rectangular block. For example, as shown in FIG. 22, when the frame is separated into rectangular blocks by alternately shifting every line in a horizontal direction, there are a dense portion (for example, a region 932) and a sparse portion (for example, a region 931) of the boundary position. In addition, variation in the image quality within the frame in which the degradation of image quality is remarkable in the dense portion of the boundary position and the degradation of image quality is not visible in the sparse portion of the boundary position occurs. Thus, consequently, the degradation of image quality near the boundary may be conspicuous.